Create get and post application routes

[ItsEricSun]

ℹ️ Issue

Closes #41

📝 Description

Briefly list the changes made to the code:

1. Added new Application routes in controller
2. Added new methods in Application service to help with this
3. Updated the fields in Application entity to be required or optional based on schema diagram
4. Updated Application Enum types to follow the schema better and to follow pre-existing values in migrations file
5. Updated migrations file to match schema diagram
6. Added Application service tests

✔️ Verification

Run backend and using swagger:
Get all applications returns nothing:

Post a new application:

New application shows up in DB:

Get all applications now returns that application:

Get application by ID also returns it:

Get a non-existent application returns error: